In a lot of period movies the husband & wife are shown to be retiring to different bedrooms at night. e.g. most movies about 1800's Britain or even pre WW-II. Or even War & Peace or Pride & Prejudice. Or The Count of Monte Cristo.
How & when did that change to them sleeping in the same room / same bed? Was the separate room custom only among the nobles & intelligentsia? Or did the commoners sleep in separate rooms too?